*BSD News Article 80797


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From: Ken Bigelow <kbigelow@www.play-hookey.com>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: EIDE support?  (possible dumb question)
Date: Tue, 15 Oct 1996 18:50:17 +0000
Organization: Erol's Internet Services
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Jerry Wieber wrote:
> 
> I'm looking at buying a Gateway 2000 Pentium Pro machine; but I'd like to
> forgo SCSI.  Does FreeBSD support any EIDE hard drives?  I'm not sure what
> the difference is betwixt IDE and EIDE at all.
> 
> Thanks for any pointers,

Don't worry -- EIDE is no problem for FreeBSD. The distinction stems
from the old ROM BIOS limits on drive parameters: 16 heads, 1024
cylinders, and 63 sectors (= 504MB). If you count the wires needed for
binary addressing, you'll find that these need 20 lines. Add in read and
write lines, master/slave control and recognition, and the needed
shielding grounds, and you have used up all 40 wires of the IDE cable.

EIDE is simply a way past this limit, so we can have these 1GB and 2GB
drives and such. You don't need to worry about it with any up-to-date
ROM BIOS and motherboard.

There is one caveat: If you split your drive among different OSes, the
ROM BIOS needs to be able to directly find the FreeBSD kernel. This
typically means that the kernel must reside entirely below the 504MB
limit. Once loaded, however, the kernel can readily access the rest of
the FreeBSD slice, wherever it resides.
-- 
Ken

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